1. Field of the Invention
The present invention relates to a cooling device for a fuel cell which can suitably cool off.
2. Prior Art
Recently, there has been developed a kind of a battery car equipped with a traction motor in place of an engine.
As one of these battery cars, a development of a fuel cell car which carries a hydrogen ion (or a proton) exchange membrane type fuel cell or proton exchange membrane fuel cell (PEMFC in abbreviation) as the power supply of a traction motor is advanced rapidly. This type of fuel cell will be hereinafter referred to as a PEM type fuel cell.
This PEM type fuel cell is formed or constructed as a stack formed by laminating a number of fuel cells as a power generation unit. Each cell has a structure constituted with a membrane-electrode assembly (MEA) sandwiched between two separators, of which one is an anode side separator having a hydrogen supply channel and the other is a cathode side separator having an oxygen supply channel.
Hereupon, as for the MEA, the anode side electrode catalyst layer and the gas diffusion layer are laminated successively on one side of the proton exchange membrane, and the cathode side electrode catalyst layer and the gas diffusion layer are laminated successively on the other side of the proton exchange membrane.
In the fuel cell car carrying a fuel cell of the PEM or other type, a cooling device to maintain temperature in the fuel cell within a certain appropriate range is provided.
As for the cooling device, there is a reference, in Japanese patent application No. 2000-155619filed in the name of the assignee of the present application, to the use of the cooling device for preventing a liquid junction phenomenon from occurring in a fuel cell. An outline of constitution of this cooling device is shown in FIG. 6.
This cooling device 50 is formed with a primary circulating passage 51 for a primary cooling system and a secondary circulating passage 52 for a secondary cooling system, through which a primary cooling liquid and a secondary cooling liquid are respectively circulated. The primary cooling liquid cools the fuel cell FC; the primary cooling liquid that is warmed accordingly is cooled by the secondary cooling liquid in a heat exchanger 58 where both the primary and the secondary cooling passages pass through.
The primary circulating passage 51 is provided with, first, a primary circulating pump 53 by which an insulating primary cooling liquid is pumped to be passed through the primary circulating passage 51, and second, a heat regulator 54 which is, for example, composed of a thermostat. An ion exchange device 55 also is provided in the primary circulating passage 51 in order to remove various ions, such as metal ions or the like contained in the primary cooling liquid.
The secondary circulating passage 52 is provided with a secondary circulating pump 56 by which a secondary cooling liquid is pumped to be passed through the secondary circulating passage 52. A radiator 57 cools the secondary cooling liquid.
In this cooling device 50, the primary cooling liquid is directly supplied to an electrode of the fuel cell FC. Accordingly, when there exist various ions such as metal ions in the primary cooling liquid, the electric insulation activity thereof is deteriorated, due to the conductivity thereof being raised remarkably.
In order to prevent the electric insulation activity of the primary cooling liquid from deteriorating, the cooling device 50 is provided with an ion exchange device 55 in the primary circulation passage 51, to remove various ions existing in the primary cooling liquid.
However, as for passing the primary liquid through the ion exchange device 55, because the internal pressure or resistance therefor is big, it is not appropriate to pass the whole of the primary cooling liquid through both the fuel cell and the ion exchange device 55 as in series.
Accordingly, the ion exchange device 55 was arranged in parallel to the fuel cell FC and separated one part of whole of the first cooling liquid was passed in the ion exchange device 55.
Hereupon, it is necessary for the primary cooling liquid to be let flow more than one fixed quantity thereof through the ion exchange device 55 in order to manage the electric conductivity of the primary cooling liquid in conventional cooling device for the fuel cell 50 mentioned above.
However, when the fuel cell FC is used as a power supply of a car, because the electric power demanded for the fuel cell is changed in various ways by large range according to each running state thereof or the like, a flow rate of the primary cooling liquid is also let be changed according to a change of electric power demanded for this fuel cell FC. Namely, the flow rate of the primary cooling liquid is allowed to increase, when the demand electricity for the fuel cell FC increases, because the fuel cell FC must be cooled all the much.
In contrast, the flow rate thereof is allowed to decrease, when the demand electricity for the fuel cell FC decreases.
Hereupon, in conventional device 50 as described above, the increase or the decrease of the flow rate of the primary cooling liquid is to be adjusted by the pressure applied by the primary circulating pump 53.
Besides, the quantity of the primary cooling liquid supplied in the ion exchange device 55 also depends on the pressure applied by the primary circulation pump 58.
Therefore, when the demand electricity for the fuel cell FC is small, because the pressure applied by the primary circulation pump 53 is also let become small, the flow rate of the primary cooling liquid in the ion exchange device 55 becomes small.
Accordingly, when the electric power demanded for the fuel cell is small, there may be the case that sufficient flow quantity cannot be secured in the ion exchange device 55 to measure and control the electric conductivity of the primary cooling liquid.
In order to solve the problem, it is good if the primary circulation liquid of necessary quantity to measure the electric conductivity is supplied or secured in the ion exchange device 55 by virtue of a certain method when the electric power demanded for the fuel cell is small.
However, when the demand electricity for the fuel cell is large, the primary circulation liquid more than needed is supplied in the ion exchange device by using this method, and thus the energy to drive the primary circulation pump 53 is wasted.
Consequently, it is an object of this invention to provide a cooling device for a fuel cell in which, even if the demanded electricity for the fuel cell is increased or decreased, and the flow rate of the primary cooling liquid supplied in the fuel cell is increased or decreasing, it is possible to have the electric conductivity controlled in the primary cooling liquid and the useless consumption of energy is reduced to the utmost as far as it can be.
The present invention is directed to address the above-described disadvantages, and there is provided a cooling device for the fuel cell in which a cooling liquid is circulated and supplied to the fuel cell for cooling the same, which cooling device comprises: a circulating pump, through which the cooling liquid circulates: a heat exchanger, in which the cooling liquid is circulated from the fuel cell is cooled; and ion exchange device or container made of ion exchanging resin, through which ions are removed from the cooling liquid; and a flow rate adjustment device that maintains a constant flow rate of the cooling liquid flowing into the ion exchange device.
In this invention, because there is the flow rate adjustment means arranged, through which the flow rate of the primary cooling liquid flowed through the ion exchange device is maintained constant, the flow rate thereof through the ion exchange device can be adjusted in a suitable constant range of all flow rates of the primary cooling liquid originated in the primary circulating pump.
Therefore, because the pressure applied by the primary circulating pump does not have to be configured in accordance with the value obtained when the flow rate of the primary circulating liquid exhibits the smallest value, useless energy consumption can be reduced.